Abstract: Effects of cultivation history of citrus orchard on structure of soil aggregates and soil organic carbon therein were studied using the spatio-temporal substitution method to explore stability of the soil organiccarbon in and carbon sequestration capacity of the orchard soil. Results show that a 30-year old orchard was 7.6%, 10.5% and 6.7%, higher than a 56-year old orchard, respectively, in content, mean weight diameter (MWD) and geometric mean diameter (GWD) of >0.25 mm water-stable aggregates (R_0.25), but.1.6% lower in fractal dimension, which suggests that soil aggregates decreased in stability with the cultivation going on. The effect of cultivation on characteristics of the soil organic carbon pool in the orchards was also quite remarkable. The 56-year old citrus orchard was 19.4% and 20%-80% higher than the 30-year old citrus orchard, respectively, in soil organic carbon storage in the 0-40 cm soil layer and in soil organic carbon storage in micro-aggregates (<0.25 mm). As organic carbon combined in micro-aggregates is protected physically, the 56-year old orchard was obviously higher than the 30-year old one in soil carbon sequestration capacity.